The number of cultivated wheat seedlings per unit area allows calculation of plant density. Wheat seedling density provides emergence data and this is useful for improving crop management. The number of wheat seedlings is typically determined by visual counts but this is time-consuming and laborious. We obtained field digital images of 1st to 3rd leaf stage wheat seedlings. The seedlings were extracted using an image analysis technique that calculated the coverage degree of the seedlings and the number of angular points of overlapping leaves. The wheat seedling quantity estimation model was constructed using multivariate regression analysis. The model parameters included coverage degree, number of angular points, variety coefficient, and leaf age. Introduction of the number of angular points increased the accuracy of the single coverage degree model. The R2 value was consistently > 0.95 when the model was applied to different varieties, indicating that the model was adaptable for different varieties. As the leaf stage or density increased, the accuracy of the model declined, but the minimum R2 remained > 0.87, indicating good adaptability of the model to seedlings with different leaf ages and densities. This method is an effective means for counting wheat seedlings in the 1st to the 3rd leaf stages.

Frequent waterlogging near anthesis is a primary constraint for wheat production in the Yangtze River Basin, China. This study aimed to identify the critical stage for waterlogging on wheat yield and its components and identify the possible factors determining this stage. In the first experiment (E1), we evaluated three varieties and initiated a 10-day waterlogging starting at the stem elongation (S1), booting (S2), and anthesis (S3) stages. In the second experiment (E2), waterlogging was applied at the stem elongation (S1) and anthesis (S3) stages and for three durations (five, 10, and 15 days). In E1, waterlogging at S1 and S2 resulted in a lower grain yield than at S3. In the second year of E1, grain yield under waterlogging at S1 and S3 was similar but significantly lower than under waterlogging conditions at S2. Waterlogging at S1 and S2 greatly decreased the kernel number per spike and 1000-kernel weight, but waterlogging at S3 only decreased the 1000-kernel weight. Moreover, different varieties did not change the stages mostly reducing grain yield and yield components. In E2, grain yield decreased with prolonged exposure to waterlogging and was significantly lower under 15-day conditions than the five-day conditions. There was no significant interaction between the stage and duration of waterlogging. Finally, our results indicate that in yield formation, a greater reliance on kernel weight instead of the kernel number per spike can contribute to a reduction in yield loss for waterlogging at S1 and S2. This study, therefore, indicates that the stem elongation stage is the most affected by waterlogging.

Lodging is an important limiting factor in wheat because it affects growth, yield and grain quality. Plant growth regulators (PGRs) are often used to restrain elongation of internodes, improve lodging traits, and protect yield potentials. An experiment was set up in the greenhouse at the Ottawa Research and Development Centre (ORDC) to study the effect of the selected PGRs (Manipulator, the active ingredient of which is chlormequat; and Palisade, the active ingredient of which is trinexapac-ethyl) on yield, stem height and morphological traits in six spring wheat cultivars (AC Carberry, AAC Scotia, Hoffman, Fuzion, FL62R1, and AW725). Both PGRs reduced plant height and caused a 6% to 48% reduction in the length of the second basal internode. The mixture of the two PGRs had a synergistic affect and made the stem shorter. The application of PGRs significantly reduced lodging, increased stem diameter, thickness, filling degree, and stem strength, and increased leaf relative chlorophyll content. However, application of PGRs significantly reduced grain yield, and the combination of the two PGRs (Manipulator and Palisade) had a synergistic effect and lowered the yield. In general, the effect of Palisade was more evident than that of Manipulator.

Nitrogen (N) is an essential nutrient element for crop productivity. Unfortunately, the nitrogen use efficiency (NUE) of crop plants gradually decreases with the increase of the N application rate. Nevertheless, little has been known about the molecular mechanisms of differences in NUE among genotypes of wheat. In this study, we used RNA-Sequencing (RNA-Seq) to compare the transcriptome profiling of flag leaves at the stage of anthesis in wheat NILs (1Y, high-NUE, and 1W, low-NUE) under normal nitrogen conditions (300 kg N ha⁻¹, corresponding to 1.6 g N pot⁻¹). We identified 7023 DEGs (4738 upregulated and 2285 downregulated) in the comparison between lines 1Y and 1W. The responses of 1Y and 1W to normal N differed in the transcriptional regulatory mechanisms. Several genes belonging to the GS and GOGAT gene families were upregulated in 1Y compared with 1W, and the enhanced carbon metabolism might lead 1Y to produce more C skeletons, metabolic energy, and reductants for nitrogen metabolism. A subset of transcription factors (TFs) family members, such as ERF, WRKY, NAC, and MYB, were also identified. Collectively, these identified candidate genes provided new information for a further understanding of the genotypic difference in NUE.